Most of the conventional box-type cooling systems incorporated in IC testers (hereinafter tester(s)) employ fans which are provided in a box like housing, wherein heat generated by an electric system of the tester is cooled by air flows generated by the fans.
In such a conventional technology, it is arranged that the fans mounted in the housing are propelled to take air into the electric system in the tester and the heated air is expelled from the housing to the room where the tester is located. However, this cooling system is disadvantageous because the room temperature where the tester is located increases as the number of the testers increases.
Therefore, in another conventional technology, a sealed box type cooling system is provided in the tester in order to solve the above problem. In this example, it is designed to control the temperature within the tester by sealing the housing and having a heat exchanger, a cooling device, and a fan therein. The fan sends air to the electric system in the housing. The cooled air passes through the heat exchanger while circulating within the sealed housing to control the temperature within the sealed housing. Therefore, this sealed housing type cooling system is more advantageous than the other cooling system which releases the heated air into the room where the tester is located. Furthermore, the sealed housing type cooling system is easier to control the temperature within the tester.
Such a conventional sealed housing type cooling system is shown in a plan view of FIG. 4A, a front view of FIG. 4B, and a left side view of FIG. 4C, respectively.
The conventional technology is explained in the following with reference to FIGS. 4A-4C. In a sealed housing 60, it is arranged that: boards 10 in which electric components are mounted are arranged on a board rack 15 in two layers; a power source unit 20 is arranged at the side position of the board rack 15; and heat exchangers 30 and 31 connected to a cooling tube 50 are provided in the lower side of the board rack 15 and the power source unit 20.
Cooling medium whose temperature is controlled circulates in the cooling tube 50. Because the boards 10 are provided in two layers in a vertical direction, plural fans 40 provided in the sealed housing 60 have to be large in order to generate sufficient air flows for the two layers. Thus, the size of the sealed housing 60 is adversely affected by the size of the plural fans 40 in that there arises a large dead space in the sealed housing 60.
Casters 62 are provided at the bottom of the sealed housing 60 for a precise adjustment of the tester position. In this conventional cooling system, since the housing is tightly sealed, the noise of the large fans 40 is not a major problem. The cooling system provides a dust free environment since the outside air never enters the tester except when the tester is opened for the repair and maintenance. The heated air will not escape from the housing because the heat generated by the electric system is transferred to the cooling medium. However, since the boards 10 are provided in two layers, a problem of temperature differences is occurred between the upper layer and the lower layer, which affects the performance of the boards 10 having high density electric components.
In other words, since the board rack 15 storing the boards 10 therein are provided in two layers, there arises a problem of difference in the cooling conditions between the upper and lower levels of the rack 15. In this structure of the conventional technology, since the cool air is sent from the lower to the upper direction, the air will be heated when it passes through the lower board 10 before coming to the upper board 10 and is further heated by the upper board 10. As a result, the temperature in the upper board is, for example, 5.degree. C. higher than the lower board. This temperature difference may deteriorate the operation of the VLSI (Very Large Scale Integrated) circuits and other electric components which are mounted on the boards 10.
Furthermore, the length of the air flow route in the sealed housing is quite large, which is about 5 meters, resulting in the temperature difference in the route. In order to solve this problem, the large sized fans 40 are provided in the housing. However, it still has a problem because as the size of the fans increases, the size of the sealed housing also increases. In addition, since the entire housing itself is intended to function as an air duct without employing a separate air duct therein, even though the housing would be tightly sealed, air often leaks.
Moreover, the conventional technology is further involved a problem in that an input/output side for connection of electric signals can be accommodated in only one side of the sealed housing due to the structural limitation of the sealed housing. This is because the cooling air circulates in three other directions with respect to the boards 10.
As technology advances, there is a high demand of installing a plurality of high density boards 10 in the tightly sealed housing, wherein the temperature difference should be controlled within a range of .+-.1.degree. C. In addition, there is a further demand that an overall size of the sealed housing should be minimized.